The present invention relates generally to packaging, and more particularly to packaging for electrically sensitive components which require shielding from electrical fields. Many electronic components such as metal oxide semiconductor devices are sensitive to electrostatic discharges when in their component form and can be damaged by electrostatic discharges prior to the components being installed in an electronic circuit.
Generally two different methods for protecting such electronic components are presently in use. Either the leads of each component are shorted together via a metal or conductive plastic polymeric sheet member, or the entire component is enclosed in a protective envelope. By and large the most popular and least expensive method is the use of a static shielding bag or pouch which is preferably transparent or semi-transparent to allow visual inspection of the packaged electronic component.
Currently there are several commercially available packaging products made from laminated sheets for electrically shielding electronic components. One of such products is an antistatic shield bag manufactured and distributed by Minnesota Mining and Manufacturing Company (3M Company). The 3M envelope or package is described in U.S. Pat. No. 4,154,344. Other U.S. Patents which show related products include U.S. Pat. Nos. 4,407,872; 4,424,900; 4,496,406; and 4,699,830. In each case, the laminated sheets which comprise the static shielding bags include one or more conductive metallized layers buried within the laminated structure. While the laminated sheets described in the aforementioned patents provide a surface resistivity sufficient to dissipate static and other electrical charges that could otherwise damage an electronic component, packages made from these sheets do not always accomplish the intended result. They often fail to do so because of breakdowns in the conductive metallized layers which occur during the fabrication steps for converting the sheets into bags or pouches.
It would be desirable, therefore, to provide a flexible, transparent laminated sheet which could be converted into a pouch or bag for packaging sensitive electronic components that would not lose its resistivity characteristics during the converting process, as well as repeated use in the field. It would also be desirable to create such a package that is transparent and capable of being sealed to itself. It would also be desirable to have a flexible sheet material which would provide a low surface resistivity for the outer structure of the bag or pouch and which would provide secondary static shielding protection in the event the resistivity of the outer structure is compromised and the static dissipation or static shielding properties are reduced, impaired or eliminated.